1. When taking photos of animals and children, get down on their level. It will give you a perspective of them that you don't normally see, and generally the photo will be more pleasing. I'm not sure where the light is coming from in that photo, but it might have been something you could have used to your advantage more if you'd taken it from a different angle.
2. Any time you have a photograph where there's a pattern or something mostly uniform, your eye will be drawn to whatever breaks that pattern or uniformity. In this case, my eye keeps going to whatever that is at the top. A simple crop would fix that.
3. If you're going to do selective color, expect resistance from the folks around here. Reason being, it's very rarely done well. In this case, you sucked the saturation out of everything but the yellows, which means the bus, the sign, and the graffiti on the mailbox are what stand out. Is there a relationship between those three things that you are trying to show?
4 and 5. Read up on the "exposure triangle" (aperture, shutter speed, ISO). A smaller aperture and longer shutter speed would have given you some streaks from the traffic that would have made these a bit more interesting. What was your reason for the different approaches to processing between 4 and 5?
6. I don't think I have any tips for this one; it's just kind of a snapshot. Maybe if you could tell us what about it makes it one of your favorites, we could give you some more specific ideas for improving.